Databases
National Center for Biotechnology Information (NCBI) http://www.ncbi.nlm.nih.gov/
ENSEMBL http://wensemblww.ensembl.org/index.html
Protein Data Bank (PDB) http://www.pdb.org/pdb/home/home.do
Domain databases
CDD http://www.ncbi.nlm.nih.gov/Structure/cdd/cdd.shtml
pFAM http://xfam.org/
SMART http://smart.embl-heidelberg.de/
SCOP http://scop.mrc-lmb.cam.ac.uk/scop/
more coming soon